Should a player not have declared himself resting, he must decide what stacks to divide, before starting to move the first stack. He can divide any, all or none of his stacks in any way he likes. But all resulting stacks must have at least three markers and one of them has to be a character-marker (not necessarily a General-marker) and one has to be an unit--marker. If this can not be ensured a stack can not be divided.
If a stack has been divided you take as many new army-markers as needed and rearrange the stack into the new stacks and place them all into the (same) tile. If the player is not able to move them they will have to be combined into one stack again at the end of the player’s round.
As soon as one stack has been moved no further stacks can be divided.
The size of the battles has to be restricted, so that the battle will not take too long (as all players will be together). The limitation in points together with the goal to have the most points in total means that the players will have to split their stacks. Even if a player has much less points in total than another player, he may fight and win, because the size of a single stack is limited. Having to divide before movement prevents problems based on the order of actions.